This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-278986 filed in Japan on Sep. 14, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile, based on an electric-photography system, which are provided with a transferring device, and more specifically relates to an image forming apparatus which is provided with a transferring device for transferring a developed image formed on a photoreceptor to a transferring member.
2. Background of the Invention
In an image forming apparatus such as a printer, a copying machine, or a facsimile (hereinbelow, collectively referred to as an image forming apparatus), that are based on a conventional electric-photography system, a transferring device having a charger line to perform corona discharge is used so as to transfer a developed image (hereinbelow referred to as toner image), that has been formed on a cylindrical or endless-belt-shaped photoreceptor, to a transferring member.
In such transferring device, ozone occurs upon performing the corona discharge. Thus, an ozone filter for removing the ozone is provided in the vicinity of an exhaust opening, and air containing the ozone in the device is exhausted via the ozone filter, so that the ozone is removed.
However, even though the ozone filter for removing the ozone is provided, there is limit in removing the ozone. Thus, it is often that a transferring device constituted of a transferring roller is used instead of the transferring device constituted of the charger line.
That is, there is provided the aforementioned transferring roller so as to be positioned close to or be in contact with a surface of the photoreceptor, and a bias (direct current) of a high voltage is applied to the transferring roller, so that the toner image formed on the photoreceptor is transferred to the transferring member. By using the transferring device provided with the transferring roller, it is possible not only to restrict occurrence of the ozone, but also to prevent transferring deviation that occurs upon transferring the toner image.
While, in an image forming process using the electric-photography system, quality (image quality) of a reproduced (formed) image is greatly influenced by (a) changes in an environment such as a temperature and humidity of a place where the device is provided, and (b) variation per hour and deterioration of respective members (for example, photoreceptor, exposure source, developer, transferring body, cleaning blade, and the like) that constitute an image forming portion for forming images.
Then, a test toner image (hereinbelow referred to as toner patch) is conventionally formed on the photoreceptor under a fixed condition, and an amount of an adhering toner (toner concentration) is detected, and feedback is carried out with respect to the image forming process, so as to prevent variation of the image quality, so that it is possible to constantly form images with proper quality.
U.S. Pat. No. 6,160,969 (Date of Patent Dec. 12, 2000), corresponding to Japanese Unexamined Patent Publication No. 219045/1990 (Tokukaihei 11-219045)(Publication date: Aug. 10, 1990), discloses a controlling method of (a) the transferring device having the transferring roller and (b) the image forming portion.
In the foregoing publication, as shown in FIG. 5, a transferring roller 52 is provided on a transferring section of a photoreceptor 51 so as to transfer a toner image formed on the photoreceptor 51 to paper P. Further, a latent image that has been exposed to laser light L is reproduced on the photoreceptor 51 as the toner image (toner patch) by means of a developing device 53, and the concentration of the toner patch is optically detected by an photosensor 54, so as to feedback a detection value to an electric-photography-process section for forming images. Note that, the photosensor 54 is provided between a developing portion for performing a developing step and a transferring portion for performing a transferring step.
However, according to the invention recited in the foregoing publication, there is the following case: the toner partially falls from the toner image (toner patch) to a surface of the transferring roller 52 when the toner image (toner patch) formed on the photoreceptor 51 passes through the transferring section, so that the toner adheres to the surface of the transferring roller 52.
Then, a conventional technique is arranged so that: at a timing at which the toner image formed on the photoreceptor 51 reaches the transferring roller 52, a bias having the same polarity as the toner is applied to the transferring roller so that the toner does not adhere to the transferring roller 52.
However, even though the bias having the same polarity as the toner is applied, a little toner sometimes adheres to the surface of the transferring roller 52. Note that, depending on (a) changes in an environment such as a temperature and humidity in or in the vicinity of the device, and (b) variation per hour and deterioration of a photoreceptive drum and the transferring roller 52, an amount of the toner that adheres to the surface of the transferring roller 52 also varies. Thus, in the worst case, the toner adheres to a backside of paper that passes through the transferring section, so that marking back is brought about.
It is known that: in order to prevent this defect, a bias having the same polarity as the toner is applied to the transferring roller 52, and the toner adhering to the transferring roller 52 is re-transferred to the photoreceptor 51, so as to perform cleaning continuously. Here, it is general to set a cleaning time to be a little longer than a time expected to be required in removing the toner.
In a case where the amount of the toner adhering to the transferring roller 52 is less than expected, there occurs the following case: the cleaning step is excessively performed though the toner has been cleaned from the transferring roller 52. Thus, respective members constituting the image forming section are unnecessarily used, which causes deterioration of the respective members, so that this brings about problems such as occurrence of abnormal sound, and troubles such as parts replacement caused by breakdown of parts.
If parts are designed so that lives of the parts are set to be longer than necessary so as to solve the foregoing problems, manufacturing cost of the parts is higher. As a result, this may cause price of the device and replacing cost of the parts to be higher. For example, in a case where a cylindrical photoreceptive drum is used as the photoreceptor, a photoreceptive material (photoreceptive layer) applied on a drum tube is gradually scraped, so that problems such as membranous decrease have influence on a life of the photoreceptive drum and image quality of a reproduced image.
While, in a case where the amount of the toner adhering to the transferring roller 52 is larger than expected, there occurs such problem that: the cleaning step is finished though the toner has not been cleaned from the transferring roller 52, and this causes the toner to remain on the transferring roller 52, so that there occurs marking back of the paper.
The present invention is made so as to solve the foregoing problems, and its object is to provide an image forming apparatus for performing the cleaning step with respect to the transferring body steadily without unnecessary motion.
In order to achieve the foregoing object, the image forming apparatus of the present invention includes: a transferring body for transferring a toner image on a photoreceptor to a transferring member; an photosensor for detecting at least either (a) concentration of a test toner image formed on the photoreceptor or (b) an amount of toner adhering to the transferring body; bias applying means for applying a bias having same polarity as toner so as to perform cleaning operation with respect to the transferring body to which the toner adheres; and controlling means for controlling the bias applying means so as to control the cleaning operation, that is performed with respect to the transferring body, in accordance with a detection value from the photosensor.
According to the present invention, the cleaning operation, that is performed with respect to the transferring body, is controlled, in accordance with the detection value from the photosensor for detecting at least either (a) concentration of a test toner image formed on the photoreceptor or (b) an amount of toner adhering to the transferring body.
Thus, an unnecessary cleaning operation is not performed, and it is possible to minimize a time required in cleaning, so that it is possible to efficiently re-transfer images to the photoreceptor in a short time. For example, it is possible to restrict damages given to parts such as the photoreceptor that constitute an image forming section.
Further, the amount or the concentration of the toner that actually adheres to the transferring body is detected, so that it is possible to grasp the amount of the toner without fail. Further, feedback can be efficiently carried out with respect to the cleaning operation according to the detection result, so that it is possible to minimize a time required in completing the cleaning of the transferring body.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.